1. Field of the Invention
The present invention relates to a method of fabricating a case accommodating a piezoelectric vibrating piece in a piezoelectric oscillator including the piezoelectric vibrating piece and a piezoelectric oscillator including a case obtained by the method, and an oscillator, an electronic appliance, and a radio clock including the piezoelectric oscillator.
2. Description of the Related Art
In recent years, mobile telephones and portable information terminal devices employ a piezoelectric oscillator using quartz crystal as a time source, a timing source of control signals, and a reference signal source. As this type of piezoelectric oscillator, various ones are offered. As one of them, a cylinder package piezoelectric oscillator formed in a nearly cylindrical shape is known.
In the cylinder package piezoelectric oscillator like this, two leads are extended from the opening of a case that hermetically seals a piezoelectric vibrating piece therein, whereby an excitation electrode provided on each of two surfaces of the piezoelectric vibrating piece can be connected to outside.
This type of piezoelectric oscillator is mounted on various electronic appliances. However, since these electronic appliances are being reduced in size year after year, also in the piezoelectric oscillator, further size reduction is demanded. In order to reduce the size of the piezoelectric oscillator, it is effective to reduce the outer diameter of the ring. To this end, it is necessary to reduce the diameters of two leads. However, in the case in which the leads are made narrower than the current form, the stiffness is decreased, and then it is likely to deform the leads in the process of fabrication. Particularly, the outer lead portions that are longer than the inner lead portions tend to become deformed. When the outer lead portions become deformed, they cannot maintain themselves in the state of being parallel with each other. Thus, the quality is degraded, and the oscillator cannot be used as a product. Consequently, it is likely to cause a reduction in yields.
In addition, in the process of fabrication, the outer lead portions are entangled with the outer lead portions of another hermetic terminal, which might temporarily stop the production line. Also in this point, it is likely to cause a reduction in yields. Particularly, the more size reduction is aimed, the more the problems might occur noticeably. On this account, in the fabricating method under present conditions, it is difficult to fabricate a piezoelectric oscillator of high yields and high quality which can be further reduced in size.
Then, a piezoelectric oscillator is provided which has a hermetic terminal with a single lead, not two leads (see Patent Reference 1 (see JP-A-2002-43886)). In other words, in the piezoelectric oscillator, the lead and a case (metal cap) are formed to make a pair of terminals, and only one lead is extended while two leads are extended from the opening of a case in the technique before.
In the piezoelectric oscillator described in Patent Reference 1, for example, a metal terminal is mounted on the case (metal cap) to facilitate electrical connection to outside. In the case in which the metal terminal is connected to the case in this manner, they are generally connected to each other with solder. However, the case is formed of a metal because the case is desired to be conductive, and the case thus has large heat capacity. Therefore, it is necessary to heat the entire case to some extent when the metal terminal is soldered to the case, and on this account, the soldering process is difficult, which is a cause that hinders facilitation of manufacture of the piezoelectric oscillator itself.